13-Dec-2019: Development of New System for Measurement of Weight

The prototype of one kilogram(NPK-57) is already available in India and placed at the National Physical Laboratory, New Delhi as per the provisions made under the Legal Metrology (National Standards) Rules, 2011.

The new definition of kilogram which has come into effect from May, 2019 and few countries have developed the system of realisation of unit of mass ‘kg’. The previous definition of kilogram was based on the mass of the international prototype ‘kilogram’ which is an artefact, however, the new definition is based on physical constant of nature. The change in the definition of kilogram will not have any implication in daily life in weighing of pharma and precious metals.

21-May-2019: India adopts new definition of kilogram

The CSIR-NPL, which is India’s official reference keeper of units of measurements has released a set of recommendations requiring that school textbooks, engineering-education books, and course curriculum update the definition of the kilogram.

The institute is also in the process of making its own ‘Kibble Balance’, a device that was used to measure the Planck Constant and thereby reboot the kilogram.

Scientists, last year, have changed the way the kilogram is defined. The decision was made at the General Conference on Weights and Measures. The new definitions came into force on 20 May 2019.

Currently, it is defined by the weight of a platinum-based ingot called “Le Grand K” which is locked away in a safe in Paris. Le Grand K has been at the forefront of the international system of measuring weights since 1889. Several close replicas were made and distributed around the globe. But the master kilogram and its copies were seen to change – ever so slightly – as they deteriorated.

In a world where accurate measurement is now critical in many areas, such as in drug development, nanotechnology and precision engineering – those responsible for maintaining the international system had no option but to move beyond Le Grand K to a more robust definition.

The fluctuation is about 50 parts in a billion, less than the weight of a single eyelash. But although it is tiny, the change can have important consequences.

Electromagnets generate a force. Scrap-yards use them on cranes to lift and move large metal objects, such as old cars. The pull of the electromagnet, the force it exerts, is directly related to the amount of electrical current going through its coils. There is, therefore, a direct relationship between electricity and weight.

So, in principle, scientists can define a kilogram, or any other weight, in terms of the amount of electricity needed to counteract the weight (gravitational force acting on a mass).

There is a quantity that relates weight to electrical current, called Planck’s constant – named after the German physicist Max Planck and denoted by the symbol h. But h is an incredibly small number and to measure it, the research scientist Dr Bryan Kibble built a super-accurate set of scales. The Kibble balance, as it has become known, has an electromagnet that pulls down on one side of the scales and a weight – say, a kilogram – on the other. The electrical current going through the electromagnet is increased until the two sides are perfectly balanced. By measuring the current running through the electromagnet to incredible precision, the researchers are able to calculate h to an accuracy of 0.000001%. This breakthrough has paved the way for Le Grand K to be deposed by “die kleine h”.

5-Feb-2019: New Scientific Standard of Kg

The prototype of one kilogram (NPK-57) is already available in India and placed at National Physical Laboratory, New Delhi as per the provisions made under the Legal Metrology (National Standards) Rules, 2011. There is no such proposal at present before the Government to achieve the new prototype of kilogram through physical constants.

The previous definition of kilogram was based on the mass of the international prototype ‘kilogram’ which is an artefact, however, the new definition is based on physical constants of nature. The change is in the definition of kilogram and will not have any practical implications.

16-Nov-2018: Kilogram gets a new definition

Scientists have changed the way the kilogram is defined. Currently, it is defined by the weight of a platinum-based ingot called "Le Grand K" which is locked away in a safe in Paris. On Friday, researchers meeting in Versailles voted to get rid of it in favour of defining a kilogram in terms of an electric current. The decision was made at the General Conference on Weights and Measures.

Le Grand K has been at the forefront of the international system of measuring weights since 1889. Several close replicas were made and distributed around the globe. But the master kilogram and its copies were seen to change - ever so slightly - as they deteriorated.

In a world where accurate measurement is now critical in many areas, such as in drug development, nanotechnology and precision engineering - those responsible for maintaining the international system had no option but to move beyond Le Grand K to a more robust definition.

How wrong is Le Grand K?

The fluctuation is about 50 parts in a billion, less than the weight of a single eyelash. But although it is tiny, the change can have important consequences. Coming in is an electrical measurement which Dr Stuart Davidson, head of mass metrology at NPL, says is more stable, more accurate and more egalitarian.

How does the new system work?

Electromagnets generate a force. The pull of the electromagnet, the force it exerts, is directly related to the amount of electrical current going through its coils. There is, therefore, a direct relationship between electricity and weight. So, in principle, scientists can define a kilogram, or any other weight, in terms of the amount of electricity needed to counteract the weight (gravitational force acting on a mass).

There's already a quantity that relates weight to electrical current, called Planck's constant - named after the German physicist Max Planck and denoted by the symbol h. But h is an incredibly small number and to measure it, the research scientist Dr Bryan Kibble built a super-accurate set of scales. The Kibble balance, as it has become known, has an electromagnet that pulls down on one side of the scales and a weight - say, a kilogram - on the other.

The electrical current going through the electromagnet is increased until the two sides are perfectly balanced. By measuring the current running through the electromagnet to incredible precision, the researchers are able to calculate h to an accuracy of 0.000001%. This breakthrough has paved the way for Le Grand K to be deposed by "die kleine h".

What are the advantages of the new system?

Every few decades, all the replica kilograms in the world had to be checked against Le Grand K. The new system, now that it's been adopted, will allow anyone with a Kibble balance to check their weights anytime and anywhere.